Date: Thu, 30 Sep 2004 22:45:02 +0200
From: Andi Kleen <ak@suse.de>
To: Matthew Dobson <colpatch@us.ibm.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>, LKML <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>, "Martin J. Bligh" <mbligh@aracnet.com>,
       Andi Kleen <ak@suse.de>
Subject: Re: [RFC PATCH] sched_domains: Make SD_NODE_INIT per-arch
Message-ID: <20040930204502.GD28315@wotan.suse.de>
References: <1096420339.15060.139.camel@arrakis> <415BC0BC.6040902@yahoo.com.au> <1096569412.20097.13.camel@arrakis>
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On Thu, Sep 30, 2004 at 11:36:52AM -0700, Matthew Dobson wrote:
> On Thu, 2004-09-30 at 01:15, Nick Piggin wrote:
> > Matthew Dobson wrote:
> > > IA64 already has their own version of SD_NODE_INIT, tuned for their
> > > extremely large machines.  I think that all arches would benefit from
> > > having their own, arch-specific SD_NODE_INIT initializer, rather than
> > > the one-size-fits-all variant we've got now.
> > > 
> > 
> > I suppose the patch is pretty good (IIRC Martin liked the idea).
> > I guess it will at least increase the incidence of copy+paste,
> > if not getting people to think harder ;)
> 
> Thanks!  Martin does like the idea, and I think Andi Kleen likes the
> idea of being able to tune sched_domains for x86_64, too.  Any comments,
> Andi?

It doesn't help me directly - what i need is the same thing 
for SD_SIBLING_INIT for the CMP changes.

But it seems I need to do some other work to properly support the K8
CMP first, so I'm defering attacking this a bit. 

> The patch is pretty simple.  I don't think it will increase any
> copy+pasting because I don't believe anyone has modified SD_NODE_INIT at
> all since it's been implemented, and certainly not for many kernel
> releases.  I think part of the reason for that is that it is currently
> impossible to tweak the values for your architecture of choice because
> modifying the values now will change EVERYONE's sched_domains timings. 
> Which is bad. :(  If anyone wants to tweak SD_NODE_INIT, they shouldn't
> be copying+pasting those values to all architectures.  Besides, IA64
> already gets their own SD_NODE_INIT to play with, why shouldn't everyone
> else! ;)

It would be nice if there was a SD_DEFAULT_NODE_INIT and a 
SD_DEFAULT_SIBLING_INIT in some generic
file that architecture code can use as a base for tweaking.
For the CMP change I currently only want to remove SD_SHAREPOWER
from SIBLING_INIT to get rid of SMT nice.

Later we'll probably want a SD_DEFAULT_CMP_INIT too that gives
generic values for a dual core. Dual cores should be soon pretty
common and tuning for them will be needed on several architectures
(ppc64, ia64, x86, x86-64, sparc, parisc? ...). But figuring out good
values for this will require a lot of benchmarking first.

-Andi

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